Stabilized pulse forming circuit including a gas tube



March 10, 1959' E. o. JOHNSON ,8

I STABILIZED PULSE FORMING CIRCUIT INCLUDING A GAS TUBE Filed June 25, 1953 Mai/2W4 Pl/lfi JL 2/ imam fg gg.

E13: 15 10 Z/ L I IWIII awn/r ill INVEN TOR.

EDWHRD l1 .Tm-msn'n 11 TTORNE Y United States Patent Application June 25, 1953; set-mm; 364,161 11 Claims. (or. 315-437 This invention relates to=a pulseformingicircuit, and particularly, to apulse forming: circuit including; a hot cathode gasv tube and a delayrline which-determines the width of the output pulse. An outputpulse is generated in response to a trigger pulse applied to the control electrode of the gas tube.

Hot cathode gas tubes are advantageously used inpulse formingv circuits becausethey have: large current carrying capacity with-a very small voltage drop across the tube during conduction. It has-ybeen found however that the output pulse generated from such a circuit is not; perfectly square but includes disturbances in the amplitude of the pulse and'van'ations in the trailing edge oftl-ie pulse These disturbances cause noisy andunstable opemtion which is very objectionable in various applicatiofins of pulse formingv circuits;

It :is an object ofthis inventionthe izircuit being characterized in providing an output pulse; which is free of I V hereiitcharacteristics of the gastube. It is anotherobject this invention-to provide an improved pulse formingi-circuit which generates a pulse having a stable trailingetlge. n

In one aspect, the invention comprises a hot cathode gas tube such as a thyratron having an anode connected through a resistor to a positive terminal of asource of uni-directional current and having acatliode connected through a resistor to ground (the negative terminal of the source of uni-directional potential). An artificial delay line is connected from the anode of the gas tube to ground. A trigger pulse is applied to the control electrode of the gas tube to initiate the generation of an output pulse across the cathode resistor, the output pulse having a width determined .by the. artificial delay line. A capacitor is connected directly across the gas tube from the anode electrode tothe cathode electrode.

The purpose of the capacitor is to prevent a rapid fall in the anode potential after the tube starts conducting and to thereby prolong the period of'timewhen an excess of. ions is created within the tube. It. has been found that when an excess of ions ispresent-within the tube the disturbances inherent in the normal operation of the tube are eliminated.

Other objects and aspects of the invention will be apparent to those skilled in detailed description taken in conjunction with the appended drawing, wherein:

Fig. 1 is a circuit diagram of a pulse forming circuit according to the prior art;

Fig. 2 is a representation of an output wave form of a pulse forming circuit such asthatshown inFig. 1;

Fig. 3 is a circuit diagram'ofa pulse forming circuit constructed according to the teachings ofthis invention and including a capacitor connected from the anode to the cathode of the gas tube; I v M Fig. 4 is another embodimentlof theinventio'nwherein an output of difierent polarity is obtained from an to provide apulse form ing circuit including. a gas tube anda delay line,v

disturbances caused by the in-' the art from the following.

which may bea thyratron has a filament (not shown),

a cathode 11, a control electrode 12, and an anode 13. The cathode li is connected through a cathode-resistor 14 to ground. The anode 13- is connected through a load resistor 15 to'the B+ terminal ofa source ofunidirectional potential (not shown). Thenegativeterminal of the source-is connected toground. The control electrode 12- isconnectedto an input terminal 16 to which atriggering' pulse is applied. The anode 13 is also connected to a three-section artificial; delay line, the first section'of which is made up of inductor 20 and'capacitor- ZLthe second section ofwhichis madeup of inductor 22 and capacitor 23 and the-third section of which is made up of inductor 24- and capacitor 25. The other end of the artificial delay line is connected to ground. An output pulse as shown in Fig.2 is obtained with respect to ground from-the cathode llof gas tube 10. The width of the output pulse is determined by the design of the delay line accordingto aformula which is well known in the art. Delay line pulse generators are shown and described following. page 238 of volume 19 entitled "Waveforms of the Radiation Laboratory Series, first editiompublished McGraw-Hill Book Co. Inc... 1949. The theory of delay lines'is set forth'in Chapter 22 of the same book. The design and construction of electrical delay lines is set forth volume 17, chapter 6, of the same series. Delay line pulse generators are shown and described in Patent No, 2,608,654, issued on- August 26,. 1952,. to I; C. Street, and entitled Pulse- Forming'Circuit. I

The output pulse may be-as shown in Fig. 2 and for purposes of discussion may be assumed to be in the order of 50 microseconds wide. Itwillbe noted from Fig.2 thatthe first few microseconds-of the pulse is'stable in amplitude and isfree 0f.noise,.that-is, free of distur bances in the amplitude of the pulse. Followingthe stable" portion of the-pulse there is a portion which is noisy and unstable. This portion of the pulse is characterized in having fluctuations in the-amplitude of'the' pulse and fluctuations which result in variation in the time at which the trailing edge of the pulse occurs. These variations alter the width of the pulse and may be very objectionable in many applications. It is believed that during the first few microseconds of the pulse, the'pulse is stable by reason of the effect of the interelect'rode capacitance of the gas tube 10. It: is believedthat-this interelectrode capacitance tends to delay the time at whichthe anode potential drops after the tube becomes conductive. The capacitance, in delaying the drop in anode potential, causes an excess of ions to be formed within the tube, and this excess of ions exists for a short period of time during which the output pulse is free of disturbances.

Fig. 3 shows a pulse forming circuit constructed in accordance with the teachings of this invention wherein-the circuit'of Fig. 1 is modified by the addition of a capacitor C connected directly through low impedance conductors from the anode 13 to the cathode 11 ofthe gas tube 10. Capacitor Chas a value of capacitance which is much smaller than the capacitance of capacitors 21 23 and 25 ofthe delay line. The three sections of the delay line are made of inductors and capacitors which are identical one with another and therefore capacitors 2 1, 23 and 25 are equal in value. The capacitor C is selected to have a value of less than /5 the value ofone of the. identical capacitors 21, 23 and 25. ln the design of a pulse circuit as shown in Fig. 3, a capacitor Cwill 2,877,386 Patented Mar. 10, 1959 oscillations are generated at Ia I fthe'values 'of' the various components in the circuit.

I stabilize theoutput wow:

I I 20; 22, and :24

" "fordampingresistori'all. I I I The value of the cathoderesistorld' is selectedtoipro I I vide a proper-impedance match for the artificial delay be selected having as small a value of capacitance as will provide: an output pulse-which is stable and free of I disturbances throughout its entire duration. If the value of the capacitor is "too small,

' not continue throughout the duration If the value of capacitor- C is too larg e,

turbing influence on the output signal irnmediately 01 lowing the trailing edgeof the output pulse. I

ringing. That is, clamped I frequency determined by of the outpufpulse.

turbancetakes the form of, a

' i I IThereforeJhe properv value forcapacltorC is one which provides'an amount of' capacitance iustlargeenoughto form throughout the duration of the output pulse.

In applications of be shunted across the capacitor C.

' line and therefore the value of resistance is iequaltothe square root of the inductance of one ofinductors :20, -22,

I or24 divided bythe. squareroot of the capacitanceof" one of. capacitorszl, 23, or 25, As is known,:the:dura I I don ofthe output pulse I is given by 1 the formula zzwiE I wherein N is the number, or sections .of the delay line, L I

I of the capacitors in the :delay line. The value of the anode resistor 15'is selected to provide a charging circuit including capacitors 21, 23, and 25 which has a time constant sufliciently short to insure that the capacitors will be fully charged up in the period of trigger pulses. The design formula customarily used requires that the time period between trigger pulses shall equal 3 to times the product of resistor and the total capacitance of capacitors 21, 23 and 25.

As stated above, the value of capacitor C can be so chosen that it stabilizes the output pulse during its entire duration. To satisfy this requirement, the circuit should be constructed with circuit elements which satisfy the following formula:

iwT ln KCER where t is the required stable period of time which normally is also the time duration of the output pulse, in microseconds, T is the tube diffusion time constant in microseconds, K is a complicated constant depending upon the tube characteristics, C is the capacitance of capacitor C in micro-microfarads, E is the 13+ voltage, and R is the line terminating resistance or the resistance of resistor 14. T, the tube diffusion time constant, depends upon the geometry of the tube 10, upon the molecular weight of the gas in the tube and upon the gas pressure. By way of example, an RCA type 2D2l thyratron tube has a value of T of about 100, and a value of K equal to about 1.42 times 10*". A circuit having a pulse duration of S0 microseconds and therefore a quiet time or stable period for 50 microseconds and including the above mentioned thyratron tube, might employ a capacitor C having a value of 470 micro-microfarads, a 8+ source of 250 volts and a terminating resistor 14 of 100 ohms. I

It will be understood that it the output pulse duration is very long, the value of capacitor C required to sta- I the pulse forming circuit Where j ringing immediately following the output pulse, even I though of small amplitude, must be prevented, a damp- I I ing resistor 30111213 I I I The'shuntingresistor is shown in Fig. 3 by dotted lines. I "The rin ging results from the interaction of the several capacitive and inductive elements in the circuit. The I I I j ringing may be dampedbyshunting a resistor across one i or more of thecapacitive and inductive elements:.- .For

example, aresistor 31 shunted across the three inductors I maytake the pla ce of and be a substitute so Iargeas to cause 'Thisdisavoided, the value of capacitor C shouldnot exccedVs I I I I thevalue-oftheindividualcapacitors 21, 23 and 25'. I I

arrangement: of the pulse I I I I forming circuit wherein the output resistor 14 is coIn- I nected from the delay. I ground tothecathode 11 of tube 10 as-shownin Figs. .1 I I is determinedin vvaluein I i I the same manner as. has been with. resistor 14 and the only difference;

circuits of Figs;

I is the inductance of each of the inductors and C is the a 1 capacitance of each o tire duration of: the pulse I I I mediately following theitrailing-edge of the pulse, or to I 1 noted that the capacitor j potential through resistor 15' 'same asresistor I put wave of by the connection oi acapaictor directly tromth'e anorie I of the gas tube to the. cathode I paeitor is effective in preventing noise and instability j I the period of time during which the anode voltage of the tube remains at. a: lIiigh I I I value immediately following the start of conduction I the capacitor is niade' sufficiently large to stabilize the output: at the tube ifor I I Ihy reason of its prolonging I throughthe tube.

jbilize the. output .pulse throughout its duration may be disturbing oscillations immediately following the trailing edge or thepulse. If this isthe case,

the stabilizing efiect 111 II a-choicemust bemadeasto whether to stabilize theen I and tolerate the ringing 'bilize only. an initial portion ofthe pulse so that the of very slight amplitude. r If ringing is tobe ringing is I Fig. 4 shows an alternative line to ground rather than from and 3. The output resistor 14' described in connection I 4 and 3 is that the polarity;ofthe.out-. :putpulse'is reversed withrespect to ground. 3 It will be the anode of the tubeto'the'cathode, the cathodebeing grounded.:i

previously described except that it is series. fed with 13+ I I I 15 I in the previous: figures. and 4 show a shunt fed system for the delay line.

I It is apparent form the. foregoing that according to I I the teachings, of this. invention, disturbances in: the out- I I tubeare prevented a circuit including a gas I I The value of the desired time period following. the initiation of conduction throu gh the tube. .Normally the capacitor may' have a value such that the output pulse of the pulse forming circuit is stable throughout its entire duration.

Whatis claimed is:

l. A pulse forming circuit comprising a gas tube including a cathode and an anode, an artificial delay line including capacitors and inductors and having terminals coupled respectively to said cathode and said anode, and a capacitor connected from said anode to said cathode, said last-mentioned capacitor having a value equal to less than /5 the value of any of the capacitors in each section of said artificial delay line.

2. A pulse forming circuit comprising a gas tube having a cathode, a control electrode and an anode, an output resistor connected to said cathode, an artificial delay line including a plurality of sections of inductors and capacitors coupled to said anode and to said output resistor, and a capacitor connected directly from said anode to said cathode, said capacitor having a value less than one fifth the value of each of said capacitors in said delay line, and means to supply a triggering pulse to said control electrode. I

3. A pulse forming circuit as defined in claim 2 and in addition a damping resistor connected across said ca pacitor.

4. A square wave forming circuit as defined in claim 2 and in addition a damping resistor connected across one or more of the inductor elements of said artificial delay line.

5. A square wave forming circuit as defined in claim 2 and in addition a damping resistor connected across one or more of the capacitor elements of said artificial delay line.

6. A square wave generator comprising, a gas tube having a cathode, control electrode and an anode, said cathode being connected to a point of reference potential, an

between h C" is directly i connected from. I

' Fig: 5 shows a timing eir'eui't'exactly the same those I I which is otherwise th I I i I of the gas tube. The Ica- I I artificial delay line including a plurality of sections of inductors and capacitors, a resistor, said artificial delay line being connected directly to said anode and to said cathode thru said resistor, an output terminal connected to said resistor, and a capacitor connected directly from said anode to said cathode, said capacitor having a value less than one-fifth the value of each of said capacitors in the delay line.

7. A square wave generator comprising, a gas tube having a cathode, control electrode and an anode, a cathode resistor coupling said cathode to a point of reference potential, an artificial delay line including a plurality of sections of capacitors and inductors, said artificial delay line being connected between said anode and said point of reference potential, means to apply a unidirectional potential to said anode and to said delay line at the end closest to said anode, and a capacitor connected directly from said anode to said cathode, said capacitor having a value less than one-fifth the value of each of said capacitors in the delay line.

8. A square wave'generator comprising, a gas tube having a cathode, control electrode and an anode, said cathode being connected to a point of reference potential, an artificial delay line including a plurality of sections of inductors and capacitors, an output terminal, said artificial delay line being connected between said anode and said output terminal, an output resistor coupled between said output terminal and said point of reference potential, and a capacitor connected directly from said anode to said point of reference potential, said capacitor having a value less than one-fifth the value of each of said capacitors in the delay line.

9. A square wave generator comprising, a gas tube having a cathode, control electrode and an anode, a cathode resistor coupling said cathode to a point of reference potential, an artificial delay line including a plurality of sections of capacitors and inductors, said artificial delay line being connected between said anode and said point of reference potential, means to apply a unidirectional potential to said anode thru said delay line, and a capacitor connected directly from said anode to said cathode, said capacitor having a value less than one-fifth the value of each of said capacitors in the delay line.

10. A pulse forming circuit comprising a gas tube including a cathode and an anode, an artificial delay line having terminals coupled respectively to said cathode and said anode and including a plurality of sections each having an inductor and a capacitor, all of said capacitors in said sections being equal in value, said sections being connected in cascade, and a capacitor connected between said anode and said cathode and having a value not exceeding one-fifth the value of each of said capacitors in said sections of said delay line..

11. A square wave generator comprising a gas tube having a cathode, control electrode and an anode, an artificial delay line including a plurality of sections of inductors and capacitors, a resistor, said artificial delay line being connected directly to said anode and to said cathode through said resistor, an output terminal connected to said resistor, and a capacitor connected directly from said anode to said cathode, said capacitor having a value less than one-fifth the value of each of said capacitors in the delay line.

References Cited in the file of this patent UNITED STATES PATENTS 2,054,882 Schlesinger Sept. 22, 1936 2,353,527 Touceda July 11, 1944 2,688,076 Richmond Aug. 31, 1954 2,724,789 Overbeck Nov. 22, 1955 

